Isolation of Arthrobacter species from the phyllosphere and demonstration of their epiphytic fitness.

Bacteria of the genus Arthrobacter are common inhabitants of the soil environment, but can also be recovered from leaf surfaces (the phyllosphere). Using enrichment cultures on 4-chlorophenol, we succeeded in specifically isolating Arthrobacter bacteria from ground cover vegetation in an apple orchard. Based on 16S rRNA gene sequencing, the isolates were found to belong to at least three different species of Arthrobacter. Compared to the model bacterial epiphyte Pantoea agglomerans, the Arthrobacter isolates performed as well or even better in a standardized laboratory test of phyllosphere fitness. A similar performance was observed with the well-characterized soil isolate Arthrobacter chlorophenolicus A6. These findings suggest that the frequently reported presence of Arthrobacter strains on plant foliage can be explained by the capacity to multiply and persist in the phyllosphere environment. As bacteria from the genus Arthrobacter are known for their ability to degrade a wide variety of organic pollutants, their high phyllosphere competency marks them as a promising group for future studies on phyllosphere-based bioremediation, for example, as foliar bioaugmentation on ground cover or buffer-zone vegetation to prevent pesticides from reaching soil, surface-, or groundwater.